Polysiloxanes, or chemically more exactly polyorganosiloxanes, are often referred to as silicones in everyday language. They belong to a group of synthetic polymers in which silicon atoms are linked together through oxygen atoms. Because of their typically inorganic skeleton on the one hand and the organic radicals on the other, polysiloxanes take an intermediate position between inorganic and organic compounds. In some way, they are hybrids and therefore have a unique range of properties, which is based, among other things, on the heat resistance and/or cold resistance as well as the electric properties of the polysiloxanes.
Processes for producing alkoxy-modified siloxanes with low viscosities are extensively described in the prior art. In these processes, triethoxy-modified siloxanes are reacted with alkoxyvinylsilanes by the direct hydrosilylation of siloxanes having a reactive Si—H group. This process is suitable, in particular, for producing polysiloxanes with low molecular weights of up to 15,000 g/mol. However, with increasing molecular weight, it becomes more difficult to achieve complete conversion of the starting materials by means of direct hydrosilylation. Polysiloxanes having a molecular weight of 50,000 g/mol or more are very difficult to produce in this way.
Polysiloxanes having an average molecular weight of up to 20,000 g/mol and a viscosity at 20° C. of about 1,500 mPa·s can be produced by equilibration processes known in the prior art. However, the reaction products obtained often have a high proportion of volatile components, which are undesirable in many applications, for example, in the electrical industry, because they may deposit on contact surfaces and thus cause failures. In order to counteract this phenomenon, the volatile components are usually substantially removed by distillation. Now, it is the object of the present invention to provide an alkoxysilane-modified polysiloxane that is obtained without a distillation step for purification. Another object is to provide a process for producing alkoxyalkylsilane-modified polysiloxanes that avoids the drawbacks of the prior art.